Toolbox / Stud bolt torque
Stud Bolt Length & Tightening Torque Calculator
Pick the flange, stud grade, lubricant and tool, and get the stud length, bolt-up torque, gasket stress check, tightening sequence and an order list ready to send with an enquiry.
Flange joint
ASME B16.5-2020 Class 300 NPS 6 / 150 NB, RF
Stud length
| Flange thickness t (each, no raised face) | 1.38 | in |
|---|---|---|
| Raised face / ring height (each) | 0.063 | in |
| Gasket installed | 0.125 | in |
| Heavy hex nut H (each) | 0.734 | in |
| Projection beyond each nut | 0.125 | in |
| Computed minimum | 4.73 | in |
| Rounded up to 1/4 in | 4.75 | in |
| Tabulated (B16.5) | 4.75 | in |
| Difference computed - tabulated | 0.00 | in |
Order basis: tabulated (B16.5 raised face column).
Torque
| Stud yield (min) | 105 ksi / 724 MPa | verified |
|---|---|---|
| Target stress | 52.5 ksi / 362 MPa | 50 % of yield |
| Area (tensile stress) | 216 | mm虏 |
| Load per stud | 78.1 | kN |
| Nut factor K | 0.13 | verified |
| Torque | 193 | N路m |
| Torque | 143 | lbf路ft |
| Torque | 19.7 | kgf路m |
Molybdenum disulphide (moly) paste. T = K F d. K printed range 0.11-0.15.
| If K is | Load vs target | Stress % yield |
|---|---|---|
| 0.110 | 118 % | 59 % |
| 0.130 | 100 % | 50 % |
| 0.150 | 87 % | 43 % |
Calibrated torque wrench: tightening factor alpha_A 1.4-1.6, stud stress 38-62 % of yield. verified
Gasket check
Spiral wound, 304 + graphite, 304 inner ring, CS outer ring (ASME B16.20 Tables SW-2.1-1, SW-2.1-4)
| Gasket sealing area | 8,317 | mm虏 |
|---|---|---|
| Gasket stress at the target load | 113 MPa (16,345 psi) | |
| Across the tool scatter | 86.7-139 | MPa |
| Typical minimum seating stress y | 68.9 MPa (10,000 psi) | verified |
| Maximum gasket stress | 207 MPa (30,000 psi) | verified |
Inside the sourced window. Maximum is the "maximum seating stress" of Piping-World and the highest-density spiral wound figure in the Lamons catalogue; it is a design ceiling, not a crush test. Low-stress styles (Flexitallic LS, Garlock EDGE) are listed at 5,000 psi by their makers. The seating stress is an ASME VIII code design value, not a service stress: confirm with the gasket maker.
Tightening procedure
- Pass 1: 30 % = 58 N路m (42.8 lbf路ft), cross pattern.
- Pass 2: 60 % = 116 N路m (85.6 lbf路ft), cross pattern.
- Pass 3: 100 % = 193 N路m (143 lbf路ft), cross pattern.
- Check pass at 100 %, stud to stud around the circle until the nuts stop turning.
Number studs 1 to 12 clockwise. Cross sequence, groups of four 90掳 apart:
1-7-4-10-3-9-6-12-2-8-5-11
Pass percentages: Flexitallic and Project Materials print 30 / 60 / 100; EPCLand 20-30 / 50-70 / 100. The sequence is a practical cross pattern; follow the PCC-1 pattern in your joint procedure.
Order list per joint
| Item | Qty | Specification |
|---|---|---|
| Stud | 12 | 3/4"-10 UNC x 4.75" (120 mm), A193 B7 |
| Nut | 24 | 3/4" heavy hex (ASME B18.2.2), A194 2H |
| Gasket | 1 | Spiral wound, 304 + graphite, 304 inner ring, CS outer ring |
Where the numbers come from
- Stud yield verified ASTM A193 / A320 / A1082 / B446 tables as printed by supplier and reference pages.
- Nut factor K verified Published K values scatter widely; K is a property of the whole joint.
- Tool scatter alpha_A verified VDI 2230 Table A8 as printed by public pages.
- Target stress verified Fraction of yield from public PCC-1 practice; no PCC-1 table is reproduced.
- Gasket seating stress verified ASME VIII Div. 1 m / y values from gasket makers and engineering sites.
- Nut pairing verified A194 grade paired with the stud.
Stud count, diameter and tabulated length come from the flange-bom tables. Full source log: src/lib/toolbox/bolt-torque/SOURCES.md.
Frequently asked questions
How is bolt tightening torque calculated?
The simple form is T = K 脳 D 脳 F: torque equals nut factor K times nominal diameter D times the target bolt load F. The flange mode sets F from a target stress in the stud; the general mode uses the fuller VDI 2230 formula with thread and under-head friction.
What is the flange bolt tightening sequence?
Tighten in a cross (star) pattern in several passes rather than going round the flange. The tool numbers the studs in a cross sequence and gives passes at 30 %, 60 % and 100 % of the target torque, then a check pass at 100 %.
How does lubricant change the torque?
Most of the torque goes into friction, so a better lubricant needs less torque for the same bolt load. Using a dry-thread torque on lubricated studs can overload them. The calculator changes the nut factor with the lubricant you pick.
How long should a stud bolt be for a flange?
Long enough to pass through both flanges, the gasket and two nuts, with a few threads showing beyond each nut. The tool computes the length from the flange thickness, raised faces, gasket and nut height and rounds it to the ordering step, and shows the length printed in the standard where there is one.
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